A procedure that has come into increasing use for diagnosing certain disease conditions is collection and analysis of a sample of the exhaled breath of a patient. Breath testing is noninvasive and can be accomplished rather easily by persons who are not highly skilled. Detection of the presence of certain gases in a breath sample has been found to be a reliable indicator of conditions such as lactose intolerance, and has potential for the diagnosis of gastric or duodenal ulcer. See, for example, U.S. Pat. No. 4,947,861.
For valid diagnostic results it is necessary that the tested breath sample consist essentially only of exhaled alveolar air, that is, air that has been resident in the alveolar space and has taken part in exchange of gases with the blood stream, as distinct from air that has remained in the so-called dead air space of the oral cavity and the trachea. A conscious adult patient will usually have little difficulty in producing a satisfactory breath sample by exhaling into a mouthpiece connected with an alveolar air collection system. Alternatively, since air from the dead air space is expelled during an initial part of each exhalation, an adult patient can usually follow instructions to blow the initial part of each exhalation into the atmosphere and then breathe into a collection bag only during the last part of each exhalation, to fill only alveolar air into the bag.
However, very young children, and adults who are unconscious, or materially distracted, cannot be expected to follow such instructions, and therefore it is desirable to provide a manually controllable selector valve whereby a technician collecting a breath sample can enable the patient to breathe ambient air during inhalation, allow the first part of each exhalation to be discarded back into the air, and cause the remainder of each exhalation to be charged into a collection bag. Since a neonate or young child has a very fast respiration rate, the valve used for this purpose should be light and compact, capable of being held and manipulated with one hand to leave the technician's other hand free for other activities, and it should be operable in such a manner that the technician does not have to possess great skill nor exercise special care for successfully synchronizing the valve with the patient's respiration cycle.
The selector valve should be designed to operate in a fail-safe manner, that is, the valve should, when operated, indicate in a positive manner that it is open for transmitting a breath sample to the collection bag, and, when the valve is released for any reason, it should automatically seal the collection bag to prevent contamination of the breath sample therein.